Ultra-high frequency discharge device



y 1957 E. D MCARTHUR ULTRA-HIGH FREdUENCY DISCHARGE DEVICE Filed Dc. 24,1952 Inventor. Eh'her- D. Mc Arthur; by w 4. 3

His Attorney.

United States Patent 9 ULTRA-HIGH FREQUENCY DISCHARGE DEVICE Elmer D.McArthur, Schenectady, N. Y., assignor to General Electric Company, acorporation of New York Application December 24, 1952, Serial No.327,724

7 Claims. (Cl. 315-537) This invention relates to high frequencydischarge devices of the type having space charge control means.

In discharge devices utilized in frequency ranges from a few hundred toa few thousand megacycles, transit time effects may limit theefiectiveness of control grids. One ifiiculty encountered is that thecurrents induced in the grid by the electrons approaching it from thecathode and by electrons moving away from the grid to the anode do notcancel each other when the transit angle is substantial. Since thiscondition may limit the power gain of the discharge device due to powerloading of the grid circuit, it is desirable to achieve grid currentcancellation in devices whose operating frequency and necessaryelectrode spacing results in substantial electron transit time.

it is, therefore, an object of the invention to provide means forreducing the power loading of the control grid circuit of a highfrequency discharge device.

it is another object of the invention to provide an improved highfrequency discharge device in which the net induced grid currrent iszero.

It is a further object of the invention to provide control grid meansfor density modulating an electron stream at high frequencies which isnot adversely affected by the electron transit time.

In accordance with my invention, a discharge device is incorporated in aconcentric line input resonator, the electron discharge path beingtransverse to the lengthwise axis of the resonator. The control grid,which may be described as a tunnel, is an opening extending through theinner conductor of the resonator having its entrance and exit endsrespectively facing the cathode and an electron permeable anodepositioned on or near diametrically opposite regions on the outerconductor of the resonator. Since the transit time or transit angle forelectrons in the grid-cathode space and the grid-anode space arerelatively large in the desired high frequency operating range, thetunnel-type grid is also made rela tively long, so that the transitangle therethrough approaches Z'rr radians or a multiple thereof. Thistransit angle is preferably measured between midpoints of thecathode-grid and grid-anode gaps. Accordingly, electrons entering thetunnel grid do not emerge until almost one cycle (or an integral numberof cycles) later, at which time the grid current induced by theelectrons leaving the tunnel will cancel that induced by the electronsthen entering the tunnel since the electric fields in the cathode-gridand grid-anode regions of the concentric conductor resonator areradially directed in opposite directions at any instant or atcorresponding cyclical points. Of course, during the electron transitthrough the tunnel grid, the electrons within the grid are shielded fromthe alternating electric field by the tunnel walls. The electron streamthus modulated passes the permeable anode in the resonator Wall and isemployed to excite an output resonator or other means responsive to thespace charge modulation.

The features of the invention desired to be protected of oscillationemployed.

are set forth in the appended claims. The invention itself, togetherwith further objects and advantages thereof may best be understood byreference to the following specification taken in connection with theaccompanying drawing, in which the single figure is a cross-section viewof an electron discharge device amplifier embodying the invention.

Referring now to the drawing, an amplifier 1 is shown in which aconcentric conductor input resonator 2 is modified so as to incorporatean electron discharge device therein. An output resonator 3 is arrangedto be excited by the modulated electron discharge from the inputresonator 2. As may be seen from the drawing, the input resonator 2 hasa hollow outer conductor 4 and a hollow inner conductor 5. The resonator2 is here designed as a foreshortened quarter wave resonator, theconductors 4 and 5 each being closed at one end and spaced from eachother while at the other end an annular slidable plunger 6 havingcontact fingers connects the inner and outer conductors. An annularclosure member 7 is suitably fastened, as by soldering, between theconductors 4 and 5 at a point beyond the position of the plunger 6 inorder to support the inner conductor. Actuating rods 8, one of which isshown in Fig. 1, are fastened to the plunger or slider 6 and extendthrough the annular end closure 7 to provide external means forpositioning the tuning slider and thus adjusting the frequency of theresonator to that of the signal source. The resonator is excited from asource of signals to be amplified, the input coupling means suitablytaking the form of a concentric conductor coupling section 9 having itsouter conductor attached to the tuning plunger and the inner conductorextending through an aperture in the plunger to form an inductivecoupling loop within the resonator cavity.

To provide the electron stream which is to be density modulated by thewave energy of the input resonator 2, a cathode It) is positioned in theouter wall 4 of the resonator at a point along the axis of the resonatorwhere the standing wave voltage is substantial for the mode in theembodiment shown the cathode it is spaced a substantial distance fromthe shortcircuited end closed by the tuning plunger 6. The cathodesuitably comprises a tubular nickel eyelet having a closed end facingthe inner conductor 5, the eyelet being insulatingly sealed andsupported from the outer resonator wall 4 by a glass sealing ring 11. Acapacitor 12 be tween the cathode and outer conductor bypasses highfrequency energy while maintaining direct current insulation. A heater13 within the eyelet is arranged to heat the cathode surface to therequired temperature for the desired thermionic emission, the heaterterminals extending from the external end of the cathode eyelet andinsulatingly sealed therethrough. Diametrically opposite the cathode isan electron permeable anode 14, which corresponds to a conventionalscreen grid, incorporated in the resonator wall 4. The anode14 is shownas constituting a wire mesh placed over an aperture in the outerconductor 4, although the conductor itself may be provided withapertures of suitable size and number to define an electrode whichpermits a substantial part of the electrons to pass therethrough.

In accordance with my invention,' a tunnel 15 through the innerresonator conductor 5 defines a path for the electrons traveling fromthe cathode to the anode 14 which is free of alternating fields. Whilein some cases the grid may be suitably defined only by the openings ineither a hollow or a solid inner conductor, it is generally desirable toprovide a tunnel grid having a sufiicient length to accommodate thedesired electrode spacings without redesign of the inner conductorof theconcentric line resonator. The tunnel is accordingly'prefera'bly definedby a section of cylindrical tubing which extends through the innerconductor 5, at right angles thereto, and is provided at either. endwith a wire mesh or other apertures for current and velocity control ofthe electron stream. Accordingly, a first grid eyelet 16 having a wiremesh on oneend is positioned at the cathode end of the tunnel cylinder15 and insulated for direct current potentials by means of a thin micaspacer 17. A conductor 18 is connected to the control grid and isbrought out for external connection through the center of the innerconductor of the resonator. Another grid cylinder 19 is provided at theother end of the tunnel and may be suitably conductively securedthereto. The direct current potential of the grid 19 may thus be variedwith respect to that of the control grid 15.

In operation, a source of heater voltage, which suitably be a battery20, is connected to the heater 13, and a grid bias voltage, suitablysupplied from a battery 21, is connected between the cathode and thecontrol grid 16. The anode 14 is placed at a positive potential withrespect to the cathode by a battery 22 connected therebetween. Since thegrid 19 is at the same direct voltage potential as the anode 14, linearacceleration of electrons within the tunnel grid is provided by apotential representing the total voltage of sources 21 and 22 which isapplied between the accelerating grid 19 and the control grid 16. Theelectron stream which passes through the electron permeable anode 14 isthus density modulated by the input signal in the cathode-grid gap ofthe input resonator 2.

Energy is extracted from the modulated electron stream by the outputresonator 3, which suitably comprises a quarter wave section ofconcentric conductor transmission line axially aligned with the spacecharge path. Its inner conductor 23 has a planar end portion facing theanode 14 and spaced therefrom to define an excitation gap. Thecorresponding end of the outer conductor 24 is conductively coupled tothe input resonator 2, preferably by an inner flange portion 25 thereofhermetically secured to the area of the conductor 4 around the anode 14.An annular slidable plunger 26, corresponding to the plunger 6 of theinput resonator, connects the inner and outer conductors and a closuredisk 7 is secured between the ends of the inner and outer conductors 23and 24. Actuator rod 28 is employed to adjust the position of theplunger or slider and thus tune the output resonator to the operatingfrequency.

Electrons passing through the anode 14 are collected on the end of theinner conductor 23 which serves as an anode or collector member, thismember having a positive potential with respect to the cathode due tothe conductive connection of the input and output resonators. Thedensity modulation of the electron stream excites the output resonator 3to provide a tanding wave therein having an amplitude varying inaccordance with the amplitude supplied to the input resonator. Theamplified output energy is coupled to the desired load by an outputcoupling means which may suitably take the form of a concentricconductor coupling section 29 having its outer conductor connected tothe tuning plunger 26 and its inner conductor extending through anaperture in the plunger to form an inductive coupling loop within theresonator cavity. Other means of utilizing the electron current orextracting energy from the modulated stream may be substituted withoutdeparting from the spirit of my invention.

Since the discharge device must operate in vacuum, a suitable vacuumenvelope is provided. By utilizing the external. conductors of the inputand output resonators as parts. of the envelope, the evacuated enclosuremay be simply formed by providing annular ring seals 30 and 31 of glassor other insulating material respectively positioned betweenintermediateportions of the conductors .5 and .4 and. between conductors 23 and 24.

Since the input resonator is very readily excited in its principal mode,the amplifier can be readily operated without critical adjustments.However, the transit time effects due to the width of the cathode-gridor cathodeanode gaps may be substantial where the gaps are physicallylarge and the electron transit time is an appreciable fraction of thealternating current period. According to my invention, the transit timethrough the grid tunnel in the inner conductor of the resonator isitself employed to counteract these effects and thus permit operation athigher power levels (because of the larger structure permitted) orhigher frequencies than otherwise available. lt may readily be seen thateven if the grid were of negligible length or thickness, the transittimes due to the intra-electrode spacings would still cause loading ofthe grid circuit. During their transit from cathode to anode, theelectrons induce a current in the grid circuit in one direction whilethey move between cathode and grid and in the opposite sense whilemoving between grid and anode. Thus the total grid current is made up oftwo currents corresponding to the influence of electrons in these tworegions. When the electron transit time is very small compared to theperiod of the alternating signal voltage these two currents are of equalmagnitude and opposite phase. Their sum is zero and the electron loadingis therefore zero. In all practical tubes operating at high frequencythis transit angle is not small and the phase of the two currents is notopposed. Therefore, the induced currents generally do not cancel andthere is a net current flow with consequent power loss in the inputcircuit.

This loss or loading is avoided according to my invention by arrangingthe transit time of the electrons through the tunnel grid 15 so thatelectrons traveling between the cathode and grid travel between the gridand anode during the same portion of a subsequent cycle of the operatingfrequency. The cycle-to-cycle electric field variations are, of course,generally negligible as compared to the field variations during any onecycle. This desired condition is substantially realized by making thetransit angle from the mid point of one gap to the mid point of anothergap equal to Zn radians (one cycle) at the operating frequency or anintegral multiple of the radians. Since the transit angle of the gapsmay be a relatively small part of 21:- radians while still beingsufficient to adversely affect the operation of a conventional dischargedevice, the electrical length of the tunnel grid itself may be seen toapproach 21r radians or a multiple thereof. The electrical length of thetunnel is preferably at least half the electron path length. Of course,electrons while within the tunnel grid do not induce grid currents orare they affected by the alternating fields, and hence they are ineflfect merely held for one or more cycles to be released at a time whenthey may cancel the transit time effects incurred before entering thetunnel grid. It should be realized, of course, that in the concentricconductor type resonator the alternating electric fields are radial andhence are oppositely directed in the two gaps of the input resonator atany given instant of time.

In order to control the transit time or transit angle within the gridwithout changing the mechanical dimensions of the tunnel, the biasvoltage from the source 21 is adjusted to either add or subtract fromthe voltage from the source 22. This controls the linear static electricfield directed from the grid 19 to the grid 16 at the opposite end ofthe tunnel.

While a specific embodiment of my invention has been shown anddescribed, it will, of course, be understood that various modificationsmay be made without depare ing from the principles of the invention. Theappended claims are therefore intended to cover'any such modificationswithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A concentric cavity resonator having an inner and outer conductor, anelectron discharge device comprising an electron emitting cathode at theinner surface of the outer conductor, an electron permeable anode at theouter conductor at a point diametrically opposite said cathode, and acontrol grid comprising a portion of the inner conductor having atransverse aperture therethrough aligned with said anode and saidcathode.

2. An electron discharge device comprising a cathode, a control gridelectrode, and an electron permeable anode aligned in that order along adischarge path, means coupling said cathode and anode in parallel forhigh frequencies, means for providing a high frequency signal voltagebetween said grid and said coupled cathode and anode to modulate anelectron beam between said cathode and said anode, and an output meanscoupled to and positioned beyond said electron permeable anode forproducing an output signal responsive to the modulation of said electronbeam, said grid comprising a shielded chamber having a length along saiddischarge path which is a substantial portion of said path length.

3. An electron discharge device comprising a cathode, a control gridelectrode, and an electron permeable anode aligned in that order along adischarge path and defining a cathode-grid gap and a grid-anode gap,means coupling said cathode and anode in parallel for high frequencies,means for providing a high frequency signal voltage between said gridand said coupled cathode and anode to modulate an electron streambetween said cathode and said anode, and an output means coupled to andpositioned beyond said electron permeable anode for producing an outputsignal responsive to the modulation of said electron stream, said gridcomprising a shielded chamber having a length along said discharge pathwhich is a substantial portion of said path length, the transit anglefor electrons of said electron stream between the mid-points of thecathode-grid gap and the grid anode gap being an integral multiple oftwo pi radians.

4. A high frequency amplifier comprising an input resonator, having aninner conductor and a hollow outer conductor concentric therewith, anelectron discharge device comprising a cathode electrode and an electronpermeable anode electrode positioned at diametrically opposite regionson said outer conductor, said inner conductor being apertured to providea control electrode tunnel extending at least half the length of theelectron discharge path between said cathode and said anode, means forcoupling said input resonator to a source of signals to be amplifiedwhereby high frequency oppositely directed radial electric fields areprovided between said grid and cathode and between said grid and anode,and an output resonator coupled to said input resonator and adapted tobe excited by the electron discharge passing through said anode.

5. A high frequency amplifier comprising an input resonator, having aninner conductor and a hollow outer conductor concentric therewith, anelectron discharge device comprising a cathode electrode and an electronpermeable anode electrode positioned at diametrically opposite regionson said outer conductor, said inner conductor being apertured to providea control electrode tunnel extending at least half the length of theelectron discharge path between said cathode and said anode and defininginterelectrode gaps, means for coupling said input resonator to a sourceof signals to be amplified whereby high frequency oppositely directedradial electric fields are provided between said grid and cathode andbetween said grid and anode, and an output resonator coupled to saidinput resonator and adapted to be excited by the electron dischargepassing through said anode, the electron transit time between themid-points of the interelectrode gaps being an integral number of cyclesat said high frequency.

6. An electron discharge device comprising a cathode, a control gridstructure, and an electron permeable anode aligned in that order along adischarge path, means coupling said cathode and anode in parallel forhigh frequencies, means for providing a high frequency signal voltagebetween said grid and said coupled cathode and anode to modulate anelectron beam between said cathode and said anode, an output meanscoupled to and positioned beyond said electron permeable anode forproducing an output signal responsive to the modulation of said electronbeam, said control grid structure comprising a shielded chamber having alength along said discharge path which is a substantial portion of saidpath length, and a source of potential coupled to said control gridstructure to cause the transit angle for electrons of said electron beambetween the mid-points of said cathodegrid gap and the grid anode gap tobe an integral multiple of two pi radians.

7. A high frequency amplifier comprising an input resonator, having aninner conductor and a hollow outer conductor concentric therewith, anelectron discharge device comprising a cathode electrode and an electronpermeable anode electrode positioned at diametrically opposite regionson said outer conductor, said inner conductor being apertured to providea control electrode tunnel extending at least half the length of theelectron discharge path between said cathode and said anode and defininginterelectrode gaps, means for coupling said input resonator to a sourceof signals to be amplified whereby high frequency oppositely directedradial electric fields are provided between said grid and cathode andbetween said grid and anode, an output resonator coupled to said inputresonator and adapted to be excited by an electron discharge passingthrough said anode, and a source of potential coupled to said controlelectrode tunnel to cause the electron transit time between themid-points of the inter-electrode gaps to be an integral number ofcycles at said high frequency.

References Cited in the file of this patent UNITED STATES PATENTS2,383,343 Ryan Aug. 21, 1945 2,423,327 Lafferty July 1, 1947 2,662,937Horvath Dec. 15, 1953

